Preparation of n-alkyl- and n-cyclo



United States Patent 3,151,122 PREPARATIGN OF N-ALKYL- AND N-CYCLO- ALKYLBKS (2-BENZOTHiAZQLESULFENItAMIDES Norman Karl Sundholrn, Middlehury, Conn, assignor to United States Rubber Company, New Yorir, FLY a corporation of New Jersey No Drawing. Filed Aug. 31, 1961, Ser. No. 135,124

Claims. (Cl. 260--306.6)

This invention relates to a method for the preparation of N-alkyland N-cycloalkylbis(2-benzothiazolesulfen)- amides. Such compounds are useful as accelerators in the vulcanization of any of the recognized sulfur-vulcanizable rubbers, natural or synthetic. Further, they have the useful property of showing good resistance to scorch, that is, they have little tendency to cause incipient vulcanization of conventional rubber stocks during process ing. An N-alkylor N-cycloalkylbis(2-benzothiazolesulfen)amide has greater scorch resistance than the corresponding mono-Z benzothiazolesulfenarnide derived from the same primary amine.

According to the present invention, N-alkyland N-cycloalkylbis(2-benzothiazolesulfen)amides are prepared by treating the corresponding 2-benzothiazolesulfenarnide under substantially anhydrous conditions with an acid having an ionization constant K, above 1X10 at 25 C., as represented, without limitation, by the equation:

wherein R is selected from the group consisting of alkyl and cycloalkyl radicals.

The N-alkyland N-cycloalkylbis(2-benzothiazolesulfen)amides have been prepared by the reaction of Z-benzothiazolesulfenyl chloride with the corresponding.

alkyl or cycloalltyl primary amine, according to the teachings of US. Patent 2,873,277 and US. Patent 2,889,331. According to US. Patent 2,873,277, the primary amine and the sulfenyl chloride are added concurrently to a reaction zone in a 3 :2 molar ratio. This requires the metering of theflow of both reactants. 2-benzo'thiazolesulfenyl chloride is prepared by the chlorination of 2-benzothiazolyl disulfide in a suitable organic liquid. When this is done on a commercial scale, a slurry, rather than a clear solution, is obtained which is difiicult to meter properly. The present process obviates this difficulty as it does not employ the sulfenyl chloride. According to US. Patent 2,889,331, the primary amine is added to the sulfenyl chloride in a 3:2 molar ratio ata temperature in the range from about -4 to about 0 C. This requires extensive refrigeration which is not necessary in the present process. i

As disclosed in US. Patent 2,860,142, N-alkyL and N-cycloalkylbis(2-benzothiazolesulfen)amides can also be prepared by reacting the corresponding N-alkylor N-cycloalkyl-Z-benzothiazolesulfenamide with acetic anhydride, propionic anhydride or butyric anhydride. For economic reasons, the mole of amine eliminated when two moles of the monosulfenamide are reacted to form one mole of the bis(sulten)amide must be readily recoverable in high yield to be used in the preparation of more monosulfenamide. In the process of this invention, the amine is eliminated generally as a sparingly soluble,

Patented Sept. 29, 1964 readily separable salt, which is obtained in near quantitative yield. The salt may be used as such in the preparation of the monosulfenamide, or the free amine can be readily recovered by simple treatment with caustic soda and distillation. In the process of US. Patent 2,860,142, the amine is eliminated as the soluble amide, which is more diflicult to separate in good yield than the salt. The amide cannot be used in this form to prepare the monosulfenamide but must be hydrolyzed to release the free amine.

Carr, Smith and Alliger, Journal of Organic Chemistry, vol. 14, p. 926 (1949), state that thiazolesulfenamides are quickly decomposed by acidic substances in aqueous solution or in dry ether with the formation of thiazolyl disulfides and the amine salts of the acids used. They found that in several experiments using N-cyclohexyl-Z- benzothiazolesulfenamide with hydrogen chloride in dry ether, a small amount of ether-soluble yellow oil was obtained, possibly 2-benzo'thiazolesulfenyl chloride, which decomposed rapidly at ordinary temperatures forming solid Z-benzothiazolyl disulfide.

According to the instant invention, it has been found that if the N-alkylor N-cycloalkyl-Z-benzothiazolesulfenamide is treated with a controlled amount of acid and the reaction medium is anhydrous, the major product is not the disulfide but the corresponding bis(2-benzothiazolesulfen)amide. The amount of acid required is approximately one-half equivalent of acid for each mole of N-substituted Z-benzo'thiazolesultenamide employed. The term equivalent is defined as the weight in grams of the substance which in its reaction corresponds to a gram-atom of hydrogen, or of hydroxyl, or half a gramatom of oxygen, or a gram-atom of a univalent ion. For acids which are polybasic, like sulfuric, less than one-half mole would be required. It is not necessary to use exactly one-half equivalent of acid per mole of monosulfenamide, but as close to the stoichiometric amount as possible should be employed. The greater the deficiency or excess of acid, the poorer the scorch resistant properties of the product, since a deficiency would result in unchanged N-substituted 2-benzothiazolesulfenamide in the product and an excess would result in 2-benzothiazolyl disulfide in the product. Both of these compounds have less scorch resistance as accelerators than the N-substituted bis(Z-benzothiazolesulfen)amide. In the case of acids which are monobasic, that is, those which have one equivalent per mole, the N-substituted Z-benzothiazolesulfenamide and acid are employed in approximately a 2:1 molar ratio. Since a bis(2 benzothiazolesulfen)- amide cannot be derived from a secondary amine, it is necessary that the 2-benzothiazolesulfenamide employed in the process be derived from a primary amine. The 2-benzothiazolesulfenamides derived from primary amines are generally prepared by the oxidative condensation of Z-mercaptobenzothiazole and the corresponding amine with sodium hypochlorite. For example, N-tert-butyl-Z- benzothiazolesulfenamide is prepared by this method in US. Patent 2,807,620.

Not all acids function satisfactorily in this reaction. Weak acids, exemplified by acetic acid which has an ionization constant K at 25 C. of 1.75 X 10- are not ap plicable. With acetic acid the major product is Z-benzothiazolyl disulfide, and the reaction which does take place is. so sluggish .at ordinary temperatures that heating is required to increase the rate. The acids employed in this -process are those having an ionization constant K above approximately 1X10" at 25C. or, in other terms, a pK of less than 3 at 25 C. The acid employed must be in anhydrous form. Where polybasic acids are employed, it is preferred that the K, of each of the acid groups is above approximately 1X10? Examples of suitable acids are hydrogen chloride, hydrogen bromide, 100% sulfuric acid, chloroacetic acid, bromoacetic acid, cyanoacetic acid, dichloroacetic acid, trichioroacetic acid, o-chlorobenzoic acid, o-bromobenzoic acid, o-nitrobenzoic acid and 3,5-dinitrobenzoic acid.

For ease and thoroughness of mixing, the reaction is best carried out in an anhydrous, inert organic solvent in which the 2-benzothiazolesulfenamide is soluble, such as benzene, toluene, solvent naphtha, chlorobenzene, carbon tetrachloride, methylene chloride, ethylene chloride, propylene chloride, mixed amyl chlorides, ethyl ether and dioxane, and mixtures of such solvents.

With the strong fast-reacting acids, such as hydrogen chloride and hydrogen bromide, it is the preferred procedure to progressively add the acid to the solution of the 2-benzothiazolesulfenamidc. This suppresses at least one side reaction, the formation of the disulfide, which takes place when a Z-benzothiazolesulfenamide is added to a strong acid. With the Weaker, slower reacting acids, such as chloroacetic acid, the order and manner of mixing the acid and 2-benzothiazolesulfenamide does not significantly affect the resulting product, although the desired reaction is probably favored to some minor extent by the above procedure.

The treatment of the N-substituted Z-benzothiazolesulfenamide may be carried out at a temperature of between -20 C. and 100 C., with the preferred temperature being between 15 C. and 40 C. The resulting N-suhstituted bis(Z-benzothiazolesulfen)amide is best isolated by distillation of the solvent after removal of the amine salt by filtration or water extraction.

The following examples are given to illustrate the invention:

Example 1 Dry hydrogen chloride was slowly passed into a stirred solution of 132 grams (0.50 mole) of N-cyclohexyl-Z- benzothiazolesulfenarnide in 850 ml. of dry benzene at 24-26 C. until the gain in weight was 9.1 grams (0.25 mole of hydrogen chloride). The addition time was about one-half hour. After completion of the addition, the mixture was stirred at 24-26 C. during one-half hour and then filtered. The residue was washed with two 100-ml. portions of benzene. The washings were added to the filtrate, and the benzene was removed to leave 106 grams of solid. Two-hour digestion of the solid with 220 ml. of acetone at room temperature followed by recrystallization from n-hexane with decolorizing charcoal treatment gave 53.7 grams of pure N-cyclohexylbis(Z-benzothiazolesulfen)amide as colorless crystals melting at 133-134 C.

Example 11 Dry hydrogen bromide was slowly passed into a stirred solution of 59.5 grams (0.25 mole) of N-tert-butyl-Z- benzothiazolesulfenamide in 500 ml. of dry toluene at 2426 C. until the gain in weight was 10.1 grams (0.125 mole of hydrogen bromide). The addition time was about 40 minutes. After completion of the addition, the mixture was stirred at 24-26 C. during 10 minutes and then filtere The residue was washed with two 50-ml. portions of toluene. The washings were added to the liltrate, and the toluene was removed to leave 39 grams of solid. Recrystallization from n-hexane with decolorizing charcoal treatment gave 25.4 grams of pureN-tert-butylbis(2-benzothiazolesulfen)amide as colorless crystals melting at 143144 C.

Example III Dry hydrogen chloride was slowly passed into a stirred solution of 44.8 grams (0.20 mole) of N-isopropyl-Z- benzothiazolesulfenamide in 250 ml. of dry methylene 4% chloride at 2426 C. until the gain in weight was 3.65 grams (0.10 mole of hydrogen chloride). The addition time was about one-half hour. The mixture was stirred for another half hour and then worked up as in Example II to give 30.0 grams of pure N-isopropyibis(Z-benzothiazolesulfen)amide as colorless crystals melting at 106- 107 C.

Example IV A solution of 16.4 grams (0.10 mole) of trichloroacetic acid in 100 ml. of dry benzene was added during minutes to a stirred solution of 47.6 grams (0.20 mole) of N-tert-butyl-Z-benzothiazolesulfenamide in 300 ml. of dry benzene at 2426 C. After completion of the addition, the mixture was stirred at 2426 C. during 3 hours and worked up as in Example I. Twenty-five grams of pure N tert butylbis(Z-benzothiazolesulfen) amide was obtained.

Example V A solution of 11.9 grams (0.05 mole) of N-tert-butyl- 2-benzothiazolesulfenamide and 2.36 grams (0.025 mole) of chloroacetic acid in 60 ml. of dry benzene was allowed to stand for 6 days at room temperature. The crude product obtained after the usual workup procedure was digested with water for 8 hours at room temperature, and then recrystallized from n-hexane and from ethanol with decolorizing charcoal treatment to give 3.2 grams of pure N-tert-butylbis Z-benzothiazolesulfen) amide.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A method of preparing N-alkyland N-cycloalkylbis(Z-benzothiazolesulfen)amides which comprises the treatment of a member of the group consisting or N-alkyland N-cycloalkyl-Z-benzothiazolesulfenamides under substantially anhydrous conditions with an acid having an ionization constant K, above 1x10 wherein approximately one-half equivalent of the acid is employed per mole of the Z-benzothiazolesulfenamide.

2. A method of preparing N-alkyland N-cycloalkylbis(2-benzothiazolesulten)amides which comprises the treatment under substantially anhydrous conditions of the corresponding 2-benzothiazolesulfenamide with hydrogen chloride in approximately a 2:1 molar ratio.

3. A method of preparing N-isopropylbis(2-benzothiazo1esulfen)arnide which comprises the treatment under substantially anhydrous conditions of N-isopropyl-Z-benzothiazolesulfenamide with hydrogen chloride in approximately a 2:1 molar ratio.

4. A method of preparing N-tert-butylbis(2-benzothiazolensulfen) amide which comprises the treatment under substantially anhydrous conditions of N-tert-butyl-Z-benzothiazolesulfenamide with hydrogen chloride in approximately a 2:1 molar ratio.

5. A method of preparing N cyclohexylbis (2-benzothiazolesulfen)amide which comprises the treatment under substantially anhydrous conditions of N-cyclohexyl-2-benzothiazole-sulfenamide with hydrogen chloride in approximately a 2:1 molar ratio.

References Cited in the file of this patent UNITED STATES PATENTS 2,321,305 Messer June 8, 1943 2,860,142 Conly Nov. 11, 1958 2,889,331 Sundholm June 2, 1959 OTHER REFERENCES Buckton et al.: Franchirnont, others, Beilstein (Hand-' buch, 4th ed), volume 2, pages 176, 181 (1920).

Carr et al.: J. Org. Chem, vol. 14, pages 92134 (1949). 

2. A METHOD OF PREPARING N-ALKYL- AND N-CYCLOALKYLBIS(2-BENZOTHIAZOLESULFEN)AMIDES WHICH COMPRISES THE TREATMENT UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS OF THE CORRESPONDING 2-BENZOTHIAZOLESULFENAMIDE WITH HYDROGEN CHLORIDE IN APPROXIMATELY A 2:1 MOLAR RATIO. 